Hydraulic back-pressure arrester



June 27, 1944- M. P. DE MOTTE HYDRAULIC BACK-PRESSURE ARRESTER Filed July 11. 1940 v2 sheets-sheet 1` June 27,1944. D- MOTTE' 2,352,256y

HYDRAULIC BAK PRESSURE ARRES TER Filed il, 1940 2 Sheets-Sheet 2 INVENTOR MABLRICE F? DE MOTTE ATTORNEY Y Patented June 27, `1944 UNITED S'IH'AI'ESy PATENT OFFICE 2,352,256 HYDRAULIC BACK-PRESSURE ARRESTEIt Maurice I. DeMotte, Indianapolis, Ind., assignor to Union Carbide and Carbon Corporation, a corporation of New Yorkd Applcation July 1 1, 1940, Serial No. 344,924

2o claims. (ci. ca -192) This invention relates to hydraulic back-pressure arresters for use inpiping systems for com-` bustible gases, such as medium pressure acetylene, for example.

It is well known that back-ashes may occur occasionally` in combustible" gas piping systems, accompanied by theipropagation of re and/or an explosive wave'backward through the mains. Such a back-flash is particularly dangerous in acetylene piping systems' because acetylene fgas frequently is combined 'with oxygengas at the point of consumption.' suchasina welding blowl pipe, and a back-flash may' causethe recession' of oxygen gas through the acetylene gas mains. Obviously, ifl oxygen were pennitted'to recede to the acetylene generator,F an' explosive mixture might be formed inthe generator hich would be extremely dangerous if ignited.

Back-hashes usually arearrested before reaching the gas generator `bym'eans of devices comprising liquid seals and'suitable check valves interposed in the gas conduits, which will permit the passage of gas freely in a normal direction, but which will prevent the reverse llow of gas beyond the arresting devices when a back-ilash' occurs. Prior hydraulic back-pressure arresters have notbeen wholly' dependable because of the entrainment of .liquidfrom the seal by gas bubbling through the liquid during normal operation,

with a consequent'gradual `reduction in the quantity of liquid in the seal. vConstant observation of the liquid level," and frequent additions of liquid, therefore. are necessary to maintain the efliciency of` such an arrester. Furthermore, al`

though water is the liquid most often employed for the seal, it sometimes is necessary to use more expensive liquids, suchy as ethylene glycol .solutions, the loss'of which entails a substantial mone tary expense. Another disadvantage of prior hy'- draulic back-pressure arresters is the location'of parts which may require frequent cleanin'gor repair, such as check valves and screens, in inaccessible places. l

It is 'the principal object of the present in-t vention, therefore, to provide hydraulic' backpressure arresters which' shall be .eflicient and dependable in operation. Another object 'isto provide a hydraulic back-pressure arrester, the fundamental principles of which may be applied to arresters designed, for unusually high gas ca/4 pacities as well as to arresters designed for low gas capacity. 'Other'objects arethe provision of a hydraulic back-pressure arrester in which liquid entrainment during the normal passage of Sas through theliquidseal is reduced to a mini- 55 mum; in which entrained liquid is effectively removed from the gas before it leaves the arrester, and isreturnedto theliquid seal; in which parts' whch'mayr'equire cleaning or repair are easily accessible; and which is simple, light, and compact yet rugged in construction, as well 'as inexpensive to manufacture andmaintain,

'Ilie above and 'other objects, and the novel features of the invention, wil1 become apparent from the following description takenwith the accompanying drawings, in which:

Fig; 1 is a side elevational View, partly broken away and in section, of one type of hydraulic back-pressure arrester embodying the invention;

Fig. 2 is an enlarged Velevational View, partly broken awayand insection, oif 'a' part of Vthe apparatus of Fig. 1; and Figs. 3 and 4 are side elevational views, partly broken away and in section, of two other-types of hydraulic back-pressure arresters embodying the invention.

As shown in Fig. 1, the hydraulic back-pressure arrester of the invention comprises an inl-et reservoir A having an inlet 'for gas and an outlet below the inlet; a main reservoir B adapted to contain a liquid seal and having an outlet for gas spaced from the liquid seal above the'normal liquid level, andan inlet for gas below the outlet and below the normal liquid level; aconduit C for -ga's,"in` cluding a check valve normally open during the passage of gas and adaptedto close under the influence of back-pressure, communicating between the outlet of the inlet reservoir A and the inlet of the main reservoirB and controlling the inlet to the latter; 'an outlet reservoir or liquid trap D having a gas outlet and a liquid outlet; a second conduit E for gas communicating between the outlet of the main reservoir B Vand the liquid trap D; anda third 'conduit F. for liquid, including a normally closed check valve for preventing liquid flow from the reservoir B 'to the trap D, communicating vbetween the liquid outlet of the Vtrap D and the main reservoir B.

More specically, the inlet reservoir A comprises a long vertical steel pipe Il, to the top or inlet end of which is threaded a suitable coupling IZ'adapted to be threaded to a gas main I3.` l The main water seal reservoir B, which has approximatelythe 'same length as the inlet 'reservoir A and is arranged in spaced parallel relation to the inlet reservoir, comprises a longvertical pipe I4 of greater diameter than the inlet reservoir A and having hollow caps ls and ls welded to its ,upperY and lower ends respectively. A liquid seal S is provided in the main reservoir B"lntermediate the inlet and outlet thereof by filling the reservoir with water or another suitable liquid to a predetermined normal level through a pipe elbow I1 welded to the side of the pipe I4 and closed by a removable plug.

Gas, such as acetylene, enters the hydraulic back-pressure arrester from the main I3 through the inlet at the top of the inlet reservoir A, flows downwardly, and leaves the inlet reservoir through a nipple I8 threaded into the outlet at the bottom of the inlet reservoir, and also connected to the upper end of the vertically arranged through-passage of a pipe T I9, the opposite-lower end of which passage provides a clean-out opening closed by a pipe plug 2i). l Gas then ows--to the main reservoir B through the horizontally arranged branch passage of the pipe T I9, a nipple 2| connecting the pipe Tv to one side of an externally located standard swing check valve 22 adapted to be held open by the normal flow of 'gas and to be closed by back-pressurea nipple 23 connecting the other side of the check valve 22' to one sideof the horizontally arranged passage of a pipe cross 24 arranged immediately below the reservoir 112,y and a vertical nipple 25 threaded into the upper end of vthe vertically arranged passage of the pipe cross 24- and made integral with the bottom of the main reservoir B by welding tothe cap I6 around an opening in the cap.

For the purpose of breaking up the stream of gas passing upwardly through the water seal to reduce liquid entrainment, a hollow cylindrical vertically arranged screen 26, having an open end and a closed end, as shown in detail in Fig.l 2, is arranged with its open end in the nipple 25 and extends well up into the reservoir B. Gas entering the open end of the screen 26 leaves throughy the numerous perforations 2'I in its side walls and passes upwardly through the liquid seal in' many well dispersed small bubbles, thus preventing excessive agitation and entrainment of the liquid. A support rod 28 lits within aY centrally arranged bore in, andv is Welded to, an imperfo'rate closure plate 29 whichv is fitted within the upper end of the screen 26 and is welded at its edges to the screen. The support rod 28 extends' vertically downwardly through the screen 26 and the vertical passage or opening of the pipe cross 24, which is aligned with the inlet tothe reservoirB. At its lower end the rod 2'8A fits within a bore in, andis welded to, a plug 30 threaded into the lower endT of the vertical passage of the pipe cross 24'. When it is desired to clean or repair the screen 26, or to drain the liquid from the reservoir B, the plug 3Q is removed from the pipe cross 24, and. the un-itary assembly of the plug, support rod, and screen is withdrawn through the nipple 25 andV the vertical pipe cross passage.

The outlet reservoir or liquid trap. D, which is arranged outside ofv and in parallel spaced rela-- tion to the reservoirs A and B, comprises along vertical pipe 3|, to one side of which, adjacent to the top of the pipe, is welded a: gas outlet nipple or conduit 32 which communicates at one end with the interior of thereservoir, and at its other end is threaded into the horizontally arranged' branchpassage of a pipe T 33. The pipe T 33: carries at the upper end of its vertically arranged through-passage a pressure relief valve 34l of standard construction, and at itsopposite. end isadapted to connect with a gas main 3.5. The outlet reservoir D may be filledA with liquid, such as water, to a predetermined level substantially the same as the liquid level in the main reservoir B, through a pipe elbow' 36 welded to the side off" 75 the pipe 3| and closed by a removable pipe plug. Gas is conducted from the main reservoir B through a U-shaped conduit E, opening from the main reservoir at a point spaced from the liquid containing portion thereof. The conduit E has a short leg which extends for a short distance into the main reservoir B through an opening in the top of the cap I5 and is welded to the cap around the opening. The other legv31f of the conduit E, which is relatively long, passes through an opening in the top of the outlet reservoir D, is welded to the top of the reservoir around the opening, and extends downwardly for a considerable distance below the outlet nipple 32 in spaced relation tothe inner wallof reservoir D. Thus, the direction'of flow of gas leaving the open lower end' of the conduit E is abruptly reversed and the velocity reduced during its passage to the outlet nipple 32, so that most of the entrained liquid drops out of suspension and collects in the reservoir D, thereby raising the level of the liquid seal therein. l v

As the level of the liquidv seal inl the outlet reservoir or trap D rises gradually, th'e pressure exerted by the liquid column increases until the pressure exerted in the conduit F on the'sideof a normally closed standard swing Ycheck valve3ll` toward the outlet reservoirD sufliciently overbalances the pressure exerted on the opposite, side of the check valve, by the column of liquid inrthe main reservoir B, to open the check valve. Liquid then flows fromthe trap Dlto'the'inle't. of the main reservoir B through a nipple-:39 secured in' the bottom of the trapandconnectedffto a pipe elbow 4D, a nipple 4I connecting the pipe' elbow to one' side of the'externallylocated check valve 38, and a nipple 42 connecting theother side of the check valve 38 to thehorizontall passage of the pipe cross 24. Whenthe level of the liquid seal in the main reservoirB rises to such la height that'y the pressure exerted thereby on the side ofthe check valve 38 toward Vthe-.reservoir B over-bal'- ances` the pressureV on its other side, the check valve swings closed. f I l I Uponl the occurrence'of a back-ilash, the burning gas and/or explosion wave recede throughf the gas main 35 at a high velocity to the reservoirs D and B where their passage isfa'rrested bythevw-atery seals, and. any burning.- gas is" extinguished, The pressurev exerted onthe' two: liquid sealsA causes' the check valve 22. in the conduit C: t'olsw'ing shutto retard as much as possiblel the passage of liquid back toward the-generator. As:'such check valves almost invariably leak tosom'e exten-t, however, and4 as the inertia of the check valve-prevents instantaneous closing,. some liquid almostalwaysV passes the'check valve and,v accumulatesi in the bottom of the inlet reservoir A, which thus insures the maintenance ofthelliquid seals by preventing the flow of: water allrthe way back. tothe generator. Excessive gas pressure in the arrester is relieved by automatically 'ventinggas' through the pressure relief valve 34. ,When.nor mal operation is resumed, the gas. entering the inlet reservoir A forces any collected water back to the main reservoir B. If .a `large quantity of liquid has beenv expelled .from thefoutlet reservoirA D by the pressure of the5back-ilash,/the seal may be replenished through the pipe elbow 36, although enough liquid usually remains' to provide a. seal which will build .up to a higher level as` entrained liquid is trapped out of the normallyv flowing gas. f

Proper positioning of the three` longA vertical. reservoirs A, B, and D in; spacecl parallel-relatim ib `each.other ismaintaned bvf-the conduits C and and by means bf. horizontal; braces, near the top of the arrester, Welded t the re'- spective reservoirs.

The form of the hydraulic back-pressure arrester. ofthe invention described above is particularly valuable yfor unusuallylarge rates. of gas flow. For example, arrestersconstructedas described have been used Vsuccessfully with acetyiene flow rates as high as. 6000 cu;v ft./h r. Two other types of hydraulic back-pressure arresters according to the present invention, which are particularly adaptable for lower rates of gas now, are shown in Figs. 3 and 4.v

Fig. 3 shows a hydraulic back-pressure arrester which may be constructed cheaply and simply from standard pipe ttings. The arrester comprises a 4vertical main reservoir 44 having an inlet for gas adjacent to its lower end, and a Vertical outlet chamber orliquidvtrapoutside ofv the main reservoir having ar gas outlet 46 in its side wall adjacent to its upper end. A gas conduit 41, which is secured .to the upper ends of both the reservoir 44 and the chamber 45, has a long leg which extends downwardly within the chamber in spaced relation to its interna] wall, for conducting. gas from a portion of the reservoir spaced from the liquid containing portion. The long leg of the conduit 41 has a downwardly opening exit a substantial distance below the outlet 46 arranged to discharge gas downwardly in the chamber 45. A liquid conduit 48 leads from the bottom of the chamber 45 to the reservoir 44 adjacent to the lower end of the latter and below `the liquid level therein to drain trapped liquid from the chamber back to the reservoir.

Gas, such as acetylene from a generator, is conducted through a main 49 to the arrester and discharged upwardly through the body of liquid 5|]` in-the reservoir 44 from the inlet 5I, which is provided with a captured-ball check valve 52. Gas which rises through the liquid seal 50 passes to the top of the reservoir 44, enters the conduit 41, and is discharged downwardly into the chamber 45 at reduced velocity. The gas then reverses its direction of flow abruptly and flows upwardly to and through the outlet 46 tothe main 53, in which a pressure relief valve 54 is connected. When the gas at reduced velocity f abruptly reverses its direction of now in the chamber 45, most of the entrained liquid drops out of suspension and falls down to the bottom ofthe chamber, from which it may pass back to the reservoir 44 through the conduit 48. f

A street elbow threaded into one end of the liquid conduit 48, and normally closed by a removable pipe plug, provides an opening or filling spout the upper level of which is higher th-an the conduit, whereby the chamber 45 and the reservoir 44 may be lled with a liquid, such as water, to the 'desired normal level, which should always be maintained higher than the top of the passage through the conduit 48 to prevent the by-passing of gas through the conduit 48 tothe chamber. 45. A drain cock 56 in the bottom of the reservoir 44 provides for draining the liquid from the reservoir, the conduit 48, and the chamber 45; and a plug 51 in the main 49 provides for. draining any accumulated liquid from the-main.

The arrester of Fig. 3 resists the passage of a back-flash 'in a similar manner to the arrester of Fig. 1.: When a backflash occurs, the check valve152 automatically closes because of the in 'Sil ` provided by the tube 6|.

creased pressure, and the liquidseal prevents passage of theback-ash past the arrester to the generator. If the pressure rises above a predetermined maximum, the relief valve 54 vents the gases to the atmosphere.

Fig. 4 shows another type of hydraulic baci;-l pressure arrester which is especially adapted for low rates of gas ilow. A reservo-ir or container 58, which is adapted to contain a body of liquid at a normal level, comprises two castings joined together as by welding (or a single casting, if desired) having an inlet passage 59 opening into its lower end. A captured-ball check valve 60 is positioned over the inlet and adapted to close the inlet except when gas is passing through the arrester in a normal direction. Two apertures extend through the top wall of the container 578, into one o f which is fitted the lower end of a vertical outlet tube 6I which terminates well above the normal liquid level, thus providing an outlet forgas from the container 58. A second vertical tube 62 nts within the other aperture and terminates at its lower end within the container below the normal liquid level to prevent the by-passing of gas. The upper ends of the vertical tubes 6I and 62 t within theA ends of the respective 1egs 6 3 and AG4 of an inverted U-shaped cross passage 65 in a head member 66, which also may be a casting, disposed above the container 58 in spaced relation thereto. The tubes 6l and 62 maybe secured .to the head member 66 and to the container 58 in any desired manner,V although bestresults have been obtained with welded or brazed joints.A y

A gas discharge conduit 61, which extends down through an aperture in the top of the casting 6 6 into thetubular chamber formed bythe leg 64 and the tube Vt2 in spaced relation to the walls of the chamber, terminates in a beveled open lower end providing a downwardly opening entrance or gas outlet'f68 arranged a substantial distance below the cross passage 65. The upper end of the discharge conduit 61 outside of the casting 65 is connected to the main 69 into which a pressure relief valve 1i) alsoisconnected.

During normal operation, gas, suchas acety iene from a generator, enters'the inlet passage 59 from the main 1l, forces the check valve 60 from its seat and bubbles up through the body ofwater or other suitable liquid 12 to the outlet Gas then flowsv up through the conduit comprising the tube 6| and the cross passage 65 and passes through the "inlet to the trap chamber formed by the portion of the tube 6 2 outside the reservoir 6l and the leg [i4r of the passage 65, wherein it flows downwardly. When the downwardly flowing gas reaches the entrance 6 8 of thedischarge conduit 61, its velocity is reduced, its direction of flow is reversed abruptly, and it passes upwardly through the conduit 61 to the main 69. Most ofthe entrained liquid drops out of suspension in thegas when the direction of flow is reversed, and is returned through the tube 62 to the main body of liquid 12. The beveled or tapered lower end of the conduit 61 provides that any liquid which may collect on the walls of the conduit will drip from the end of the conduit only at the lowermost point, thus insuring .that the flowing gas will not pick up the separated liquid again. Thus, it is apparent that the conduit 61 and the' upper portion of the tube 62 form a liquid trap outside of the reservoir 58,. and that this trap has an outlet conduit for liquid in communication with the reservoir. y y

The container 58 may be lled with liquid to the normal level throug-h the iilling opening' 'I3 in the side wall of the container, whichv is closed by a removable plug. Liquid may be drained simultaneously from the container 58 and the inlet passage 59 through separate drain ducts or passages 14 and 15, respectively, opening into an internally threaded single common drain passage which is normally closed by a threaded plug 161. The plug I6 has a tapered inner end which fits in and closes the passage T5, thereby preventing communication between the two drain ducts 'M and 15. A lock nut 'I'I onthe outer end' of the plug I6 compresses a gasket 18 against the out'- side wall of the container 58 to stop liquid from leaking out. When liquid is to be drained out, it is only necessary to remove theplug 16, thereby opening the common drain passage and the duct 15.

Back-flashes are arrested by the check valve 60 and the liquid seal 12 in the same Way as in the arrester of Fig. 3, any excessive pressure being relieved by the venting of gas through the relief valve 10.

From the foregoing description, it is evident that there have been provided simple yet eilicient and dependable hydraulic back-pressure arresters wherein the loss of sealing liquid is reduced to a minimum, and wherein all parts requiring frequent cleaning or repair are easily accessible.

What is claimed is:

1. A hydraulic back-pressure arrester comprising a reservoir having a portion adapted to contain a body of liquid at a normal level, said res.-

ervoir having an inlet for gas below such normal 3 level, and an outlet for gas spaced from said liquid-containing portion; a check valve controlling said inlet so constructed and arranged as to prevent the back ow of uid therethrough; a

liquid trap outside of said reservoir having an l outlet for liquid in communication with said reservoir, said trap also having an outlet for gas; and means establishing communication between the outlet of said reservoir and said trap for conducting gas to said trap.

2. A hydraulic back-pressure arrester comprising an inlet reservoir having an inlet for gas; a main reservoir having a portion adapted to contain liquid at a predetermined normal level; conduit means communicating between said inlet reservoir and said main reservoir, and opening into said main reservoir below the normal levelof such liquid; a check valve preventing the reverse flow of iluid through said conduit means to said inlet reservoir; a liquid trap outside of said main reservoir having gas outlet means and liquid outlet means; conduit means opening from said main reservoir at a point spaced from such liquid-containing portion and communicating between said main reservoir and said trap for conducting gas to said trap; and conduit means communicating between the liquid outlet means of said trap and said main reservoir.

3. A hydraulic back-pressure arrester comprising an inlet reservoir havingv an inlet, and an outlet below said inlet; a main reservoir having an outlet, and an inlet below said outlet, said main reservoir being adapted to contain liquid at a level above said last-named inlet; a conduit communicating between the outlet ofr said inlet outlet, and a liquid outlet below said gas outlet; a second conduit communicating between the outlet of said main reservoir and saidI outlet reservoir, said conduit extending intosaid outlet reservoir and terminating below the gas outlet thereof and above the liquid' level therein; a third conduit communicating between the liquid outlet of said outlet reservoir and the inlet of said main reservoir; and a normally closed check Valve in said third conduit adapted to open when the pressure on the side thereof toward said outlet reservoir becomes greater than the pressure on the opposite side thereof'.

4. A hydraulic back-pressure arrester as claimed in claim 3, also comprising means for filling said main reservoir and said outlet reservoir with liquid to predetermined levels.

5. A hydraulic back-pressure arrester as claimed in claim 3, alsocomprising means for relieving excess pressure in said arrester.

6. A hydraulic back-pressure arrester as claimed in claim 3, also comprising screeny means arranged to break up a stream of gas discharged intosaid main reservoir through the inlet thereof whereby such gas will pass upwardly through such liquid in well-dispersed small bubbles.

7. A hydraulic back-pressure arrester comprising an inlet reservoir having anl inlet, and any outlet below said inlet; a main reservoir having an outlet, and an inlet below said outlet, said main reservoir being adapted to contain liquid at a level intermediate said last-named inlet and outlet; a conduit communicating between the outlet of said inlet reservoir and the inlet of said main reservoir; a check valve in said conduit adapted to befclosed by back pressure; a liquidA trap having a gas outlet and a liquid outlet; a conduit communicating between the outlet of said main reservoir and said trap for conducting gasto the latter; a conduit communicating between the liquid outlet of said trap and said main reservoir for returning trapped'liquid to the latter; a check valve in said last-named conduit for preventing the flow of liquidv from said main reservoir to said trap, said check valve being adapted to permit the flow of fluid through said last-named conduit from said trap when the pressure on the side, of said check valve toward said trap exceeds the pressure on the opposite side thereof; a screen in said main reservoir below the liquid level therein arranged so that gas from said first-named con.- duit will nass therethrough; means providing an opening in said arrester; a plug engaged in said opening; and a. support member secured to said plug and to saidy screen, said screen` and said support member being removable through said opening as a unitary assembly with said plug.

8. In a hydraulic back-pressure arrester, a reservoir adapted to contain liquid, said reservoir having an outlet, and an inlet below the level ot such liquid; a conduit communicating with said inlet; a check valve. controlling said inlet so constructed and arranged as to prevent. the back flow of' lluid therethrough; a screenmember arranged inA said reservoir below the liquid level therein so that gas from said inlet will' pass through said screen member; means providing an opening adjacent to the bottom of said arrester for drawing liquid" therefrom; a plug engaged insaid opening; and a support member secured to said plug and" to said screen member, said screen member and said support member being' removable through said opening as a unitary assembly with said plug.

9. A hydraulic-back-pressure arrester comprising I..reservoir having a portion adapted to contain a body o f 4`liquid@ati ya normal level, 'andan inlet for gas belowsuchlevel; aV check valve in said reservoir adapted lto Vprevent the backow of fluid through "said-inlet; meansv providing a;

chamber outside of said reservoir; a conduit establishing communication between the lower portion of said chamber and said-reservoir below such level for returningtrapped liquidto said reservoir; a conduit for conducting gasfrom a portion of said reservoir spaced fromy said liquidcontaining portion,` said conduit `havingan end in said chamber arranged'to discharge gas downwardly therein; and said chamber having an 'outlet for gas above saidend of said conduit.

10. A hydraulic'A back-pressure arrester 4comprising a reservoir Ahaving av portion adaptedto contain a body ofliquid ata normal level',v said reservoir having an vinlet for gasl below such liq'- uid level; means providing a tubular Achamber having Van open-flower end terminating `insaid reservoir below'fsuch liquid level, said Chamber having an inlet foifgas above said lower end, a

conduit establishing communication betweenv said last-namedinletanda portion of said reser- Voir spaced fr ornsaijd liquid-containing portion; and a conduit for condu-cting vgas from said chamber, said ylast-named conduit having ya downwardly opening entrance'in said chamber below said last-named inlet.

l1. A hydraulic back-pressure arrester comprising a container adapted to contain a body of liquid at a normal level; a gas supply conduit opening into said container adjacent to the bottom thereof; a check valve in said supply conduit; a head member above said container in spaced relation thereto, said head member having a cross passage therein; a tube secured to said head member and to said container, said tube establishing communication between the upper portion of said container and one side of said cross passage for conducting gas to the latter; a second tube secured to said head member and to said container in communication at its upper end with the other side of said cross passage, said second tube having an open lower end terminating in the lower portion of said container below such normal liquid level; and a gas discharge conduit secured to said head member and extending downwardly within said second tube in spaced relation to the inner wall thereof, said discharge conduit having a downwardly opening entrance below said cross-passage.

l2. A hydraulic back-pressure arrester comprising a reservoir; an inlet for gas adjacent to 'the bottom of said reservoir; an outlet for gas adjacent to the top of said reservoir; a check valve controlling said inlet; a liquid trap comprising a chamber having an outlet for gas; a conduit connecting the outlet of said reservoir to said chamber, said conduit extending downwardly in said chamber below the gas outlet of the latter; and a second conduit connecting together said chamber and said reservoir adjacent to the lower ends thereof; said liquid trap being provided with a llin-g spout the upper level of which is higher than said second conduit.

13. In a hydraulic back-pressure arrester, a reservoir adapted to contain liquid; a gas inlet passage for introducing gas into said reservoir below the level of such liquid; a check valve between said inlet passage and said reservoir; a single drain passage for draining liquid from said reservoir and said inlet passage simultaneously;

separate drain ducts leading from said reservoir and said inlet passage to said single drain passage; and mean-s inV said single drain passage normally closing the same and also closing one' of lsaid drain ducts, thereby preventing communicationbetween said drain ducts, said last-named means being operable to open said drain passage and saidiclosed drain duct for draining liquid fromt'said reservoir and said inlet passage.

14. Afhydraulic back-pressure arrester having a reservoir adapted to containa body of liquid,

said reservoir having a gas inlet below the level of such body of liquid and a' gas outlet above such level; a check valve controlling said inlet so constructed and arranged as to prevent the back end, oner of said conduits being in.communica-v tion with said gas outlet of said reservoir, the

other of said Aconduits acting to conduct gas from said chamber. j

i 15. In a hydraulic back-pressure arrester, a reservoir havingl a portion adapted to contain a body of'liquid, said reservoir havingga gas outlet spaced from saidliquid-containing portion, and a gas inlet below the level of such body of liquid; a conduit for supplying gas to said inlet, said conduit having an opening therein aligned with said inlet; a tubular screen arranged in said inlet and extending into said reservoir, said screen having an open lower end, perforate side walls, and an imperforate closure adjacent to the upper end thereof; a plug removably secured in said opening; and a rod secured to said imperiorate closure and to said plug, said rod passing through said screen in spaced relation to the side walls thereof and projecting through said open lower end; said screen and said rod being removable from said arrester through said inlet and said opening as a unitary assembly with said plug.

16. A hydraulic back-pressure arrester comprising a reservoir having a portion adapted to contain a body of liquid, said reservoir having a gas inlet below the normal level of such body of liquid, and a gas outlet spaced from said liquidcontaining portion; a check valve controlling said inlet so constructed and arranged as to prevent the back flow of fluid therethrough; a liquid trap having a liquid outlet and a gas outlet; a conduit establishing communication between the gas outlet of said reservoir and said trap for conducting gas to said trap; and a conduit establishing communication between said liquid outlet and said reservoir below the level of such body of liquid.

17. A hydraulic back-pressure arrester comprising a reservoir having a portion adapted to contain a body of liquid, said reservoir having a gas inlet below the lnormal level of such body of liquid, and a gas outlet spaced from said liquidcontaining portion; a liquid trap having a liquid outlet and a gas outlet; a conduit establishing communication between said gas outlet of said reservoir and said trap for conducting gas to said trap; a conduit establishing communication between said liquid outlet and said reservoir for returning trapped liquid to the latter; and a normally closed check valve in said last-named conduit adapted to open when the pressure on the side thereof toward said liquid trap becomes greater than the pressure on the opposite Vside thereof.

-18. A hydraulic back-'pressure arrester comprising .a reservoir having a portion ladapted to contain a vbodyfoi liquid, .said reservoir Ahaving a gas inlet below lthenormal ylevel of such body `of liquid, and a gas'outlet :spaced from said liquidcontaining portion; -means providing a chamber having a wall, `the lower 4portioniof said-chamber being in communication with said reservoir for returning yliquid thereto, the upper Aportion `of saidchamber having afgas-inlety-a'conduit establishing communication .between said gas Ioutlet of said reservoir and said gas inlet of .said charnber; and Aafconduit for-discharging gas -from said chamber extending xdownwardly therein in spaced relation to said wall, Aand lhaving the `lower end [thereof below said -gas inlet of vsaid chamber, said lower end being tapered.

-19. A hydraulic back-.pressure arrester cornprising a .main reservoir having .a .portion adapted to contain abody of liquid, said main reservoir having agas inletbelow the normal 'level ofvsuch body of liquidfandia-gas outlet spaced from said liquid containing portion; an .outlet reservoir adapted to contain liquid, said Voutlet .reservoir havingia gas outlet, fand a liquid outlet belowlsaid gas'outlet; a conduit rcommunicating between the outlet-of said main vreservoir and :said outlet .res-

data ;eno

ervoir, said conduit extending into said outletv reservoir and terminating `below the l:gas outlet thereof andabove'the liquid level therein; a conduit establishing communication between :said liquid outlet and said main .reservoir for returning trapped liquid to thelatter; and a normally closed check valve lin.sali;1.last-named conduit adapted to open when the pressure on the side thereof toward said liquid trap Abecomes .greater than the ,pressure onlthe opposite side thereof.

V20. A hydraulic back-pressure .arrester :comprising a .reservoir `having .a .portion adapted to contain a body of liquid, .-.saidreser-voirhaving .a gas inlet below the normal llevel of.such body of liquid, and a gas outlet ,spacedfrom .said liquid containing portion; ya .gas vsupply conduit .connected `into said inlet; .a liquid trap .'havingaliquid outlet anda gas outlet; aconduit establishing communication between fsaid gas .outlet Aof said reservoirvand said trap for conducting gas to lsaid trap; a conduit establishing :communication between said liquid0utlet and saidiinletrof said reservoir .for returning Ytrapped .liquid Ato said reservoir; and a normally closedicheck valve in said last-named conduit adapted to yopen when the pressure von .the side .thereof .toward said liquid trap becomes greater than the pressure on .the opposite side thereof.

MAURICE'P. DEMOTTE.

CERTIFICATE OF CORRECTION. Patent No. 2,552,256. Y June 27, 191m.

MAURICE P. YDE MOTTE.

It is hereby certified that error appears in of the above numbered patent requiring correction as follows: Page 2, first column, line 55, after the word "arranged" insert "below the liquid level; and second column, line l5, after "of" insert -the page )4, second column, line 68, claim 8, for "drawing" read -draining; page 5, first column, line 22, claim lO, after "end" strike out t he comme. and insert instead a semicolon; andthat the said Letters Patent shouldbe read with this correction therein that the same may conform to the record of the cas Patent Office.

the printed specification e in the signed and sealed this 5th day of september, A. D. 19ML.'

Leslie Frazer (Seal) Acting Commissioner of Patents. 

